The present invention relates to a transmission and more particularly to a constant mesh variable gear ratio transmission spanning the range from a low gear ratio to direct drive.
Transmissions have been used for many years in a variety of environments including automobiles, trucks and other moving vehicles when a variety of gear ratios is required. Hydraulic transmissions typically utilize fluid couplings to connect an engine drive shaft to a transmission output shaft. Fluid couplings typically experience significant energy losses. Oil or other hydraulic fluid with which the coupling is filled is directed from an impeller driven by the engine between the vanes of a turbine. The oil drives the turbine at an increasing speed until the turbine rotates at the same speed as the impeller. Although a fluid coupling can provide a smooth takeup so that the vehicle moves off without jerking, a significant amount of energy can be lost in this fluid coupling.
Hydraulic tranmissions typically also include two planetary gear sets employing a centrally mounted pinion and one or more planetary gears which engage with the pinion and with the teeth on the inside of an annular ring gear commonly known as an annulus. The transmission of force through the transmission is accomplished by the planetary gear sets and the fluid coupling. A specific number of pre-determined stepped gear ratios are typically provided by using friction clutches to selectively lock the sun gear, the annulus or the planet gears separately or in various combinations. There can be additional energy losses in the friction clutches used to control the motions of these various gears. An example of this type of transmission is shown in U.S. Pat. No. 2,624,215 to McRae. It is apparent that transmissions using fluid couplings and friction clutches can be inefficient and complicated to manufacture and maintain. Because they also tend to be large and heavy and inefficiently consume power, they are not well suited for use in the more compact lightweight automobiles that are becoming more and more prevalent. Furthermore, because of the energy losses experienced in such transmissions, it is often difficult to match the most feasible gear ratio to the horsepower output of the engine and the applied load.
Large and inefficient transmissions would tend to overtax the smaller engines that are presently used more and more frequently and, thus, significantly reduce engines efficiency and increase gasoline consumption.
One such new lightweight and efficient engine is disclosed in my U.S. Pat. No. 3,876,342. There is a need for more efficient transmissions that will be more compatible with such new engines. The more efficient use of energy, the weight and material savings resulting from the use of the engine and transmission will have a cumulative similar effect in the vehicle in which they are installed.
Some transmisson mechanisms use hydraulic systems rather than friction clutches to control the motion of various elements of their planetary gear sets to provide different gear ratios; see for example U.S. Pat. Nos. 3,008,341 to Cobb and 3,240,083 to Stoddard.
The elimination of friction clutches may increase the efficiency of the transmission somewhat but the use of large amounts of hydraulic fluid, sometimes under high pressure, to operate these systems is a further source of transmission inefficiency.